I will forward here the information I got on another forum. It's about two nice little freeware modules called CumulusX and Simprobe.
WHAT IS IT ?
CumulusX is a module that will create thermals in the FSX world.
Simprobe is a module that analyse in real time the landscape and the wind around you, to dertermine where CumulusX should create thermals, in a realistic manner.
Note for FS9 users: simprobe will not work on FS9. BUT CumulusX is also designed to work with some kind of pre-computed maps to determine where to create thermals. In the end, it's the same, it's just that simprobe does it dynamically, without downloading any map.
PREREQUISITES:
You need FSX SP2 (for the FSX version with simprobe, that is), .NET Framework 2.0, and I don't remember what else. Everything is explained in details on the homepages.
WHERE TO GET THEM:
Follow these links

http://www.luerkens.homepage.t-online.de/peter/
(scroll down to find the FS9 version)
http://carrier.csi.cam.ac.uk/forsterlew ... index.html
TROUBLESHOOTING:
If CumulusX! crashes at startup (with an error like "system.invalidoperation"), you are probably using FSX Acceleration. You have to perform the following steps:
- uninstall Acceleration
- install SP1
- install SP2 (CumulusX! should work properly at this point)
- uninstall SP2
- install Acceleration
Worked for me
